Flowability of rutile pigment

ABSTRACT

The flowability of fine particle size, rutile titanium dioxide is improved by uniformly mixing 0.05-2% by weight of naphthenic acid with the titanium dioxide.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation-in-part of copending application Ser. No.972,971, filed Dec. 26, 1978 now abandoned.

DESCRIPTION

1. Technical Field

Fine particle size rutile TiO₂, which is used primarily in plastics, isfrequently shipped in rail cars to large consumers. Historically, thismaterial has been difficult to unload when shipped in bulk. It has nowbeen found that treating the TiO₂ with naphthenic acid improves the flowcharacteristics of the pigment which facilitates the unloading of TiO₂from rail cars.

2. Background Art

Generally, commercial grades of TiO₂ are coated with hydrous oxideswhich improve the durability and gloss of pigments. These coatings,however, do not render the pigment free-flowing. Some pigments, e.g.,those used in the plastics industry, are not specially coated. Theseuntreated or uncoated pigments are generally of fine particle size andpossess much poorer flowability than treated pigments. Frequently, thepigment becomes compacted into a nonflowing mass by the vibration of therail car it is transported in. Historically, mechanical methods havebeen employed to assist in unloading cars. Generally, cars arepressurized and the pigment is blown out. In that case, pressurizing thecar forces material immediately above the exit hole to dislodge but doeslittle to move surrounding pigment. Rail cars have been modified toallow gases to be blown in at strategic places to dislodge the pigmentand vibrators have been installed, but these mechanisms have met withlimited success and, all too frequently, the pigment must be dislodgedfrom the walls of the car by manual shoveling.

It has now been found that treating the TiO₂ pigment with naphthenicacid improves the flow characteristics of the pigment which facilitatesunloading of pigment in bulk shipments, such as rail cars.

DISCLOSURE OF THE INVENTION

Accordingly a fine particle size, rutile titanium dioxide pigmenttreated or coated with 0.05-2% by weight of naphthenic acid based on theweight of titanium dioxide has been found which possesses improvedflowability as compared to uncoated pigment.

The coated pigment with improved flowability is prepared by a processcomprising injecting at a high velocity a gas stream into aconveyer-pipe treatment chamber while atomizing naphthenic acid into thehigh velocity gas stream, thereby providing a zone of turbulence, addingparticulate TiO₂ into the zone of turbulence, supplying a low velocitygas stream at the inlet to the conveyer-pipe treatment chamber parallelto the high velocity gas and conveying the gas, naphthenic acid and TiO₂through the conveyer-pipe treatment chamber, the ratio of high velocitygas to low velocity gas being more than 3:1.

The treatment or coating of the titanium dioxide particles withnaphthenic acid must be accomplished with an apparatus that providesuniform mixing of very small amounts of materials with very largeamounts of different materials in particulate form. Such an apparatuscomprises a conveyer-pipe treatment chamber with an entrance end and adischarge end, a nozzle for introducing a mixture of a high pressure gasand the naphthenic acid housed within the conveyer-pipe treatmentchamber and means for feeding particulate titanium dioxide into anopening in the conveyer-pipe treatment chamber at the feed end, saidnozzle comprising an inner tube, from which the naphthenic acid exits,concentrically arranged within an outer tube to form an annular openingbetween the outer tube and the outside surface of the inner tube fromwhich the high pressure gas stream exits, said opening in the feed endof the conveyer-pipe treatment chamber located to permit particulatetitanium dioxide to enter above the nozzle, said nozzle positioned sothat the longitudinal axis of the nozzle and the conveyer-pipe treatmentchamber coincide and so that the nozzle discharge end is beneath theopening to the conveyer-pipe treatment chamber and within a verticalprojection of the opening area, the entrance end or the discharge end ofthe conveyer-pipe treatment chamber having means to cause a flow of lowpressure gas toward the discharge end of the conveyer-pipe treatmentchamber. The mixture exits from the conveyer-pipe treatment chamberuniformly mixed.

The present invention can also be described by referring to the FIGUREwhich is a schematic drawing of the apparatus.

DESCRIPTION OF THE DRAWING

Referring now to the FIGURE, conduit 22 is connected to feed opening 8and is equipped with a rotary valve 7 mounted within conduit 22. Screwfeeder 9 is connected to supply chamber 10 and on the discharge side toconduit 22. Particulate material enters through supply chamber 10 and istransported and metered by the screw feeder 9 to conduit 22 throughrotary valve 7 which provides a seal against gases from conveyer-pipetreatment chamber 5, into conveyer-pipe treatment chamber 5 abovenozzle 1. The material to be mixed with the particulate material entersthrough tube 2 which discharges within tube surface 4 at a controlledrate. A gas under high pressure is supplies through pipe 3 and exitsnozzle 1 at a high velocity which atomizes or disperses the materialfrom tube 2. Blower 6 supplies a gas at low velocity to the entrance end21 of conveyer-pipe treatment chamber 5. Nozzle 1 is mounted in thecenter of conveyer-pipe treatment chamber 5, preferably directly underopening 8, preferably so that the end of the nozzle 1 is at the verticalcenter line of the opening 8. The particulate material encounters a zoneof turbulence generated by the discharge of nozzle 1. The turbulencesubjects the material from tube 2 to shear forces that disperse and mixit intimately and finely with the particulate material. The mixture ispneumatically conveyed to the discharge end 20 of the conveyer-pipetreatment chamber 5.

Generally, uniform mixing can be obtained with gas velocity ratios ofhigh velocity to low velocity of more than 3:1. Preferably, the ratio ofhigh velocity to low velocity is 4:1-10:1.

Conveyer-pipe treatment chamber 5 is generally circular in cross sectionbut may also have a square, oval or other shape. Likewise, opening 8 mayhave a circular, oval, rectangular or other cross sectional shape.

Blower 6 can be eliminated and a fan or similar apparatus used at thedischarge 20 of conveyer-pipe treatment chamber 5 to suck gas into theentrance end. In such a case, rotary valve 7 is not needed.

The material that exits tube 2 is the material that is relatively smallin amount compared to the particulate material that is fed to 10 and maybe in solid, liquid or slurry form. The only requirement is that thehigh velocity gas is able to move the material through the nozzle exit.The high velocity gas disperses this material into particles that aredeposited on the particulate material uniformly.

The velocity through the throat of nozzle 1 is 300 ft/sec or greater.Generally, the high velocity gas is discharged from nozzle 1 at 300-2000ft/sec (90-600 meters per second) and the low velocity gas at 80-100ft/sec (24-30 meters per second). Thus, about 4-33% of the total gasflow entering chamber 5 is at high velocity.

The following test assesses the relative flowability of TiO₂ pigmentwhich correlates with actual experience in unloading covered rail hoppercars. A 0.25 m³ cylindrical hopper is equipped with a 10 cm dischargehole, air slide and vibrator at the bottom. A 70 kg sample of thepigment to be tested is charged to this hopper. The sample and hopperare then shaken for four hours on a special shaker table which subjectsthe hopper to the acceleration forces encountered in rail and trucktravel. This shaking compacts the sample in the hopper.

The flowability properties of the pigment is then tested by unloadingthrough the discharge port with both air slide and vibrator actuated. Afree-flowing pigment is one which readily discharges from the hopper.Pigments which bridge or rat hole will not freely discharge and must bescooped or rodded from the hopper.

Pigments, which are most benefited by naphthenic acid treatment, arerutile, fine particle titanium dioxides. The use in the present processof titanium dioxide without any coating results in a greater improvementin flowability than when the surface is previously coated. Wet treatmentprocesses are commonly used to improve the durability of titaniumdioxide by coating them with hydrous oxides. The present process is notmeant to exclude additives used to facilitate processing, such asmicronizer aids, prior to coating with naphthenic acid. By "fineparticles" is meant having a mean particle size of less than 1 micron.Preferred particles are those that have an average diameter of fromabout 0.15-0.25μ. This fine particle pigment is particularly useful inthe plastic industry because of its high strength and good dry-blenddispersibility. It is theorized that the poor flow properties of pigmentare more pronounced in fine particle pigment because of an increase invan der Waals forces.

The pigments are treated with from 0.05-2.0% by weight of naphthenicacid based on the pigment. It has been found that 0.05% by weight isneeded to significantly improve the flow characteristics. Too muchnaphthenic acid adversely effect the flow properties of the pigment andthe properties of the pigment in the end-use for which it is intended.More than 2% by weight of the naphthenic acid does not result in theimproved flow characteristics of this invention.

Pigments that have hydrous oxide coatings generally require 0.05-0.1% byweight naphthenic acid based on the weight of pigment. Pigments thathave no hydrous oxide coatings generally require 0.1-2% by weightnaphthenic acid based on the weight of pigment.

Naphthenic acid refers to a class of acids derived from petroleum,particularly that of a non-paraffinic character. They are usuallymonocarboxylic and monocylic and completely saturated. The most commonare derivatives of cyclopentane, such as C₅ H₉ COOH and similarderivatives of cyclohexane and cycloheptane and their homologs.Commercial naphthenic acids, which are a mixture of the above acids, aresuitable for use with this invention.

The naphthenic acid should be applied after the final grinding of thepigment as earlier application may cause discoloration of the pigment.The acid must be applied with the apparatus described herein andillustrated in the FIGURE in order to achieve a thorough mixing of theacid and pigment.

The following examples further illustrate the invention. All parts,percentages and proportions that may appear in the examples are byweight unless otherwise indicated.

COMPARATIVE EXAMPLE A

An untreated TiO₂ pigment having a mean particle size of less than 1micron was spread out to a depth of 1 cm on a tray. A total of 0.14 kgof naphthenic acid was uniformly sprayed on 70 kg of sample TiO₂pigment. This sample was then collected and blended for 30 minutes in aV-cone blender. It was tested for flowability according to thepreviously described test. It would not freely discharge from the testhopper due to rat holing. A 70 kg sample of the same pigment withoutnaphthenic acid was also tested for flowability. Its flowability was thesame as the treated sample, that is, it was not free-flowing.

EXAMPLE 1

The apparatus illustrated in the FIGURE having a tube 12 3/16 inch (4.8mm) O.D. and 1/8 inch (3.2 mm) I.D., a nozzle 1 1.315 inches (33.3 mm)O.D. and 1.049 inches (26.6 mm) I.D., a twin screw feeder 9, a Youngrotary valve 7, an opening 8, 4 inches (101.6 mm) in diameter intoconveyer-pipe reaction chamber 5 which was 4.5 inches (115 mm) O.D. and4 inches (100 mm) I.D. and 60 ft (18 m) in length was used to mixnaphthenic acid with titanium dioxide in fine particulate form.Naphthenic acid feed dissolved in alcohol was metered through tube 2while titanium dioxide in particulate form was metered through feeder 9.Blower 6 provided low pressure air and nozzle 1 provided high pressureair.

The apparatus was used to treat the same type of untreated pigment usedin the Comparative Example. Samples treated as described were found toflow freely when tested for flowability. Additional tests were made withthe apparatus at naphthenic acid concentrations of 0.05-2.0%. Allsamples in which greater than 0.2% naphthenic acid flowed freely whileuntreated samples and samples treated at less than 0.2% naphthenic aciddid not flow freely from the test hopper.

EXAMPLE 2 (BEST MODE)

Twenty tons of the TiO₂ were treated by the apparatus described inExample 1 with 0.3% by weight naphthenic acid based on the TiO₂. Seventykg samples were collected at periodic intervals during this testing.These were all evaluated on the flowability test and were found to befree-flowing.

EXAMPLE 3 (BEST MODE)

A TiO₂ pigment having 1.2% alumina and 0.8% silica surface treatmenthaving a mean particle size less than 1 micron was treated with 0.03-2%by weight naphthenic acid as described in Example 1. This pigmentwithout naphthenic acid was found to have poor flowability. The treatedpigment of this example was tested for flowability and the samples with0.05-0.1% by weight naphthenic acid flowed freely. All others were notfree-flowing.

EXAMPLE 4

In order to demonstrate that treating pigment with naphthenic acidfacilitates the unloading of rail cars, treated and untreated pigmentwas loaded into separate compartments of a rail car.

The untreated pigment was 20 tons of R-101® (a commercially available DuPont uncoated rutile titanium dioxide pigment of fine particle sizecontaining about 0.30% triethanolamine). The untreated pigment wasloaded into one end compartment of a three-compartment rail car. Therail car was an 80-ton Model PD-4000 manufactured by the North AmericanCar Corp. The center compartment was left empty.

Twenty tons of R-101® were treated with 120 lbs of naphthenic acid(Commercial Grade 200 purchased from Exxon Corp.) giving an averagetreatment of 0.3% weight percent naphthenic acid on pigment. The treatedmaterial was loaded into the other end compartment of the rail car. Therail car was then shipped by rail approximately 240 miles.

The rail car was unloaded using standard techniques by pressurizing therail car with air (max 15 psi). An air driven rotary vibrator (Model No.380, manufactured by Vibco Corp.) was attached to the hopper beingunloaded. After 7 hours approximately 65% by volume of the treatedpigment had been unloaded. In contrast, after 7 hours only about 35% byvolume of the untreated pigment had been unloaded.

INDUSTRIAL APPLICABILITY

The naphthenic acid coated TiO₂ of this invention is useful in normalpigment applications and permits easier unloading of rail cars of TiO₂that have been compacted during transit from one site to another. Theprocess of the invention is the method of mixing uniformly naphthenicacid and TiO₂ at the levels described herein to achieve improvedflowability.

We claim:
 1. A method of improving flowability of bulk, fine particlesize, rutile titanium dioxide pigment that facilitates unloading ortransferring said pigment comprising injecting at a high velocity a gasstream into a chamber while atomizing naphthenic acid into the highvelocity gas stream, thereby providing a zone of turbulence, addingparticulate titanium dioxide having a mean particle size less than 1micron into the zone of turbulence, supplying a low velocity gas streamat the inlet to the chamber parallel to the high velocity gas andconveying the gas, naphthenic acid and titanium dioxide through thechamber, the ratio of high velocity gas to low velocity gas being morethan 3:1 and the amount of naphthenic acid is 0.05-2% by weight based onthe weight of titanium dioxide.
 2. A method of improving flowability ofbulk titanium dioxide that facilitates unloading or transferring of thetitanium dioxide comprising introducing a mixture of naphthenic acid anda high pressure gas through a nozzle into a conveyer-pipe treatmentchamber, feeding particulate titanium dioxide into an opening in theconveyer-pipe treatment chamber at the feed end located to permit thetitanium dioxide to enter above the nozzle, said nozzle positioned sothat the logitudinal axis of the nozzle and the conveyer-pipe treatmentchamber coincide so that the titanium dioxide falls in to a zone ofturbulence created by the high velocity gas stream and transporting thegas, titanium dioxide and naphthenic acid to the discharge end of theconveyer-pipe treatment chamber with a low pressure gas that enters thechamber parallel to the high pressure gas said naphthenic acid beingadded in sufficient amount to provide a coating on the titanium dioxideof 0.05-2% by weight based on the weight of titanium dioxide.